Excess heat from synthesis gas (syngas) exiting from a reformer is removed by waste heat boilers. Sodium sublimate at 823° C., and subsequently leaches from the heat resistant, refractory, lining bricks of the reformer. The sodium cause sodium fouling, in the form of sodium carbonate deposits in the waste heat boilers. Sodium carbonate could be used as a heat insulator, hence its deposit in the waste heat boiler tubes lowers the heat removing capacity. In order to remove the sodium carbonate from the waste heat boilers, in accordance with prior art methods, the whole reformer train needs to be shut down for about six days. During the shut down, the reformer train need to be cooled to ˜40° C. to allow personnel to enter the waste heat boilers, who use brushes to get rid of sodium carbonate. It is an objective of this invention to minimise the shut down period of the reformer train while removing the sodium carbonate from the waste heat boilers. It is a further objective of this invention to avoid re-hydration of the refractory bricks during shut down to avoid weakening of the refractory bricks and an extended dry out procedure of the bricks before start-up of the reformer train. This had been a problem during prior art methods of sodium removal.